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3-2_3. presentation 8
1. On the Selection of the Type of
Pipes for Water Distribution
Networks
Boyan Borisov
UASEG - Sofia
2. The current situation
⢠Pipes are basic elements of Water Distribution
Networks /WDN/ and single pipelines
⢠Polyethylene /PE/ and ductile cast iron /DCI/â two
of the most widespread pipe materials for water
supply pipelines
⢠The current situation with the selection of pipe
material in practice
3. Outline of presentation
⢠1. Short history and descriptions of compared
pipe materials
⢠2. Description of the selection methodology and
quantitative and qualitative parameters
⢠3. Analysis of some of the compared parameters
⢠4. Discussion and conclusions
4. A short description of compared
materials
1. Ductile cast iron /DCI/
2. Polyethylene /PE/
5. Comparison methodology
Weight Rating for Valuation Rating for
Valuation for pipe
N Parameter coefficie pipe mat. for pipe pipe mat.
mat. j+1
nt j mat. J j+1
Parame Vi,j =
i Ki Rij Ri,j+1 Vi,j+1 = Ki.Ri,j+1
ter i Ki.Ri,j
i+ Parame Vi+1,j = Vi+1,j+1 =
1
Ki+1 Ri+1,j Ri+1,j+1
ter i+1 Ki+1.Ri+1,j Ki+1.Ri+1,j+1
Parame Vn,j =
n Kn Rn,j Rn,j+1 Vn,j+1 = Kn.Rn,j+1
ter n Kn.Rn,j
6. The quantitative parameters
1. Initial investment
min (Ci , j ; Ci , j 1 )
1. Purchase costs Ri , j
2. Construction costs Ci , j
2. Whole life costs Ci,j â the value of âinitial
1. Initial investment investmentâ or âWLCâ for
2. Operation and pipe type âjâ
maintenance cost
7. The chosen comparison parameters:
qualitative ones
3. Environmental aspects
4. Corrosion resistance for DCIP
and slow crack growth
resistance for PE Rating âRâ is
5. Impact resistance between 1 and 3
6. Thermal stability
Weight
7. Durability
coefficient is
8. Operational experience between 5 and
9. External load resistance 15%.
10. Resistance to water hammer
8. Parameter 1 - Initial investment
1. Price characteristics of both types of pipes
âŹ/mâ Turning point
phenomenon
DCI
PE DN
9. Parameter 1 - Initial investment and
turning points of pipes and pipelines â
real data
10. Parameter 2 â Whole Life Cost
N
Ct
WLC t
t 1 (1 r /100)
⢠After initial investment the energy
consumption, i.e. head losses is decisive factor
⢠An analysis is made for the influence of pipe
roughness and the internal diameter
11. Influence of hydraulic roughness
Hydraulic roughness PE pipes DCIP
Pipes;
k1=0.01mm k1=0.03mm
âIndividual conceptâ
Pipelines and networks;
k2=0.1mm k2=0.1mm
âGlobal conceptâ
⢠In transition zone friction factor âfâ is slightly
influenced
⢠Difference in head losses for k=0.01 and k=0.3
is under 5 %
12. Influence of internal diameter
⢠Difference by 1 % in internal diameter causes
difference in head losses by 5 %
⢠There are bigger differences in internal
diameters of different pipe materials, incl. PE
and DCI
15. Environmental aspects
⢠Raw materials:
ďź for DCI pipes fresh iron ore or iron scrap
ďź for PE pipes: oil
⢠Carbon print
g of CO2 eq/1 m g of CO2 eq/1
Type g of CO2 eq/per
(DN 110 or DN m (DN 630 or
of pipe kg of pipe/year
100) /year DN 500) /year
PE 40.1 88.23 2819
DCI 20.7 246.33 1900
Note: The data is for the production and laying stage,
without transportation.
16. Durability for DCI and PE
⢠DCI pipes: the service life is so long that it is
even not mentioned in the product standard
⢠Thinner wall since 2010 and rubber gaskets
⢠PE pipes: the standard service life declared in
EU is 50 years; in some standards â 100 years
⢠There are now PE pipes which are 50 years old
and are in good condition
17. Summary - Qualitative parameters
Qualitative parameters DCI (K x R) PE (K x R)
3. Environmental aspects 5% x (2-3) 5% x (1-2)
4. Corrosion resist. for DCI 5% x (1-2) 5% x (2-3)
and slow crack growth for PE
5. Impact resistance 5% x (2) 5% x (1)
6. Thermal stability 5% x (3) 5% x (2)
7. Durability 10% x (2) 10% x (2)
8. Operational experience 5% x (1-3) 5% x (1-3)
9. External load resistance 5% x (2-3) 5% x (1-2)
10. Resist. to water hammer 5% x (2-3) 5% x (2)
18. Discussion
⢠In practice - tendency for exaggeration of some
disadvantages and advantages of the pipes;
⢠Standards, technical literature and own research
should be used instead manufacturerâs catalogues and
common opinions
⢠It has been confirmed that generally PE is appropriate
for smaller diameters and DCI for larger ones
⢠Consensus of stakeholders is needed for ratings of the
qualitative parameters and all weight coefficients
19. Conclusions
⢠Qualitative parameters still could be decisive
for the selection of pipe material
⢠The result of the comparison methodology
could vary in the course of time and for each
particular case
⢠The comparison methodology could be used
for all pipe materials
20. Next step
⢠The selection methodologies have to be
included in some form in the national design
legislation or gradually to be accepted as a
good practice